XATTRs don't persist after document body replace / upsert operation

const string key = "xattrs_demo";

const string createBy = "jack";

_bucket.Remove(key);

_bucket.Insert(key, new {name = "mike"});

_bucket.MutateIn<dynamic>(key)

    .Upsert("_data.created_by", createBy, SubdocFlags.CreatePath | SubdocFlags.AttributePath)

    .Execute();

_bucket.Replace(key, new {name = "michael"});

_bucket.LookupIn<dynamic>(key)

    .Get("_data.created_by", SubdocFlags.AttributePath)

    .Execute();